The long term objective of this project is to delineate mechanisms by which behavior influence brain structure and function. Our strategy is to focus on a well characterized behavior with known adaptive functions - the endocrine-stimulating vocal behavior. This proposal is an extension of a previous finding that neurosecretory hypothalamus receives axonal projections from the vocal control midbrain and the marginal auditory thalamus. We now propose to further these findings by verifying acoustic properties, characterizing neurochemical properties of these pathways, and exploring the functional role of these projections. We will be using antidromically evoked extra-cellular recordings, anterograde tracers, retrograde tracers and immunohistochemical double- labeling methods to test the hypothesis that the afferent and efferent projections of the accessory auditory thalamus that we have discovered are in fact acoustic responsive, met-enkephalin positive pathways. We further postulate that estrogen receptors co-localize with (1) the met- enkephalin positive cells in the midbrain that give rise to terminal projection into the accessory auditory thalamus and (2) the met- enkephalin positive cell groups in the marginal thalamus. Finally, we will use opioid receptor agonist and antagonists, ovariectomy and hormone replacement study to explore the role of enkephalin and estrogen in the vocal signals induced endocrine changes. The proposed studies will provide the neural mechanisms whereby an individual's own vocal behavior and environmental sounds can influence the endocrine state of the individual. It is hoped that this line of work will serve as a model for future research on the subject of acoustic environment and health issues.